1. Field of the Invention
The present invention relates to a pattern edge detecting method and a pattern evaluating method.
2. Related Background Art
A method for detecting an edge of an evaluation pattern and evaluating a shape of the pattern has been widely used in various industrial fields. For example, in order to manufacture a semiconductor device with a high yield ratio, it is required to precisely measure a fine pattern, which is formed by a photolithographic process, a film forming process, and an etching process. In the conventional art for a pattern measurement, the edge of a pattern is detected in an image obtained by an imaging device of a SEM type, which is called a critical dimension scanning electron microscope (CDSEM), the detected edge coordinates are digitized, and desired information for an evaluation pattern is obtained. As a method for detecting the edge of a pattern, a threshold method has been used in the conventional art. However, in addition to the threshold method, various detecting methods including an improved threshold method are proposed, and a CD of a pattern is measured using these methods (for example, Japanese Patent Laid-Open Pub. No. 1997-174714). In the description below, a problem in the conventional art that uses a pattern edge detecting method based on the threshold method is described, but the same problem may be generated even when the other edge detecting methods are used.
In a pattern edge detection using the threshold method, it is required to set a region called a region of interest (ROI) to a pattern. By designating a portion of a pattern whose edge is to be detected by the ROI, a desired measurement value is obtained based on the detected partial edge coordinates. On the assumption that a simple pattern, such as a line pattern, a space pattern or a hole pattern, exists in the ROI, an edge detecting process is executed. At this time, it is required to designate a pattern that exists in the ROI. When the ROI is set, ROI, an accurate pattern measurement is enabled. The reason is that an adaptable threshold method is different according to a kind of a pattern. In the case of a manual measurement, the ROI is generally set by a real-time operation of an operator. However, since it is difficult to visually differentiate a line pattern and a space pattern from image information, a time and effort are required to transmit information on an inspection pattern as an order to the operator. This situation is also applicable to the case of an automatic measurement. A pattern is measured using a coordinate value previously set in a recipe as ROI instead of real-time setting by the operator. The ROI is set by a recipe creator in preparing the recipe, and there remains a problem that the recipe creator is required to know information of a pattern in advance.
In order to resolve the above-described problem, by using a method disclosed in Japanese Patent Laid-Open Pub. No. 2006-234588, it may be conceivable to determine whether a pattern within a ROI is a line pattern or a space pattern by referring the pattern with design data thereof. However, even when this method is used, an assumed pattern does not always exist in the ROI. For example, when a pattern is omitted due to a manufacture failure of the pattern or the pattern is not resolved, there arises a problem that the edge may be erroneously detected.
Meanwhile, a method for detecting the edge of a pattern without the ROI is also proposed (for example, Japanese Patent Laid-Open Pub. No. 2003-178314). The method disclosed in Japanese Patent Laid-Open Pub. No. 2003-178314 has an advantage that the entire edge of a pattern as well as the local edge of the pattern can be detected without setting the ROI. However, if a method based on a kind of image filtering is used, two pairs of edges corresponding to a top edge and a bottom edge of the pattern may be detected. There is a problem that a desired pattern edge cannot be obtained so long as information on an inspection pattern is not referred to using any means.